First I'm not sure this is in the correct area, if not, mods feel free to move it to the right board.

So here is the problem, its weird how this works.
My buddy has a 92 firebird 305 v8. When he lets his firebird warm up, he gets heat, but if he takes off after only a few minutes, it will not heat at all, not even when the car is warmed up it just keeps blowing cold. The car is not overheating and runs fine. The heater core can't be clogged up because it will give heat when he lets it sit for awhile and warm up.

We are unsure if its the sensor or the control box... We've even swapped the sensor and nothing, even shut the car off for a few, and turned it back on and let it sit and still blows cold.

Any ideas?

 

It's probably none of that. It's probably just physically keeping the coolant at a cool temperature due to the thermostat rating being low, or the tstat being stuck open.
Does this engine have a mechanical radiator cooling fan or an electric fan on the radiator? If it's electric, make sure it is not running all the time.

Normally if your temp gauge works on the dash you can see how hot the coolant is when the engine is running. If the gauge says 160*F, then that's why your heater isn't getting hot. To get hot air from your heater you want a 195* tstat, and you should see around 200*F on your temp gauge after the engine warms up.
In some cold climates some people have to use a grille or radiator block, - something simple like putting a piece of cardboard between the radiator and A/C condenser to block part of the air flow.

 

It has an electric fan on the radiator, and a 195*F tstat. Its not the fan or tstat, and the coolant is hot, because both hoses are hot.

 

What temperature is "hot"? did you check the hoses and radiator with a IR temp-gun?
Assuming the coolant is 200*F, then you should check your two heater hoses where they connect at your firewall.
Are they also 200*F with no blockage?
You can check for blockage by pulling the heater hose from the fitting on the firewall. Disable your distributor and have someone use the key to crank the engine over. You might want to check both sides to eliminate blockage inside your heater core.

If that's good, then you could have a problem with the HVAC vacuum control that switches between the A/C core and the heater core. There is a rotary vacuum switch right behind your HVAC control panel.
It distributes vacuum via tiny tubes to the valves that control how the blower air flows past the cores.

 

Well, as I said, I don't see how it can be clogged when it gives heat after letting it sit to warm up when its cold. If he takes off when its cold, it gives no heat at all.. The control box is used, he replaced it last winter. He is going to replace it again and see if that is the problem. If that is not it, we will check the HVAC.